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'Zombie' satellite runs amok in Earth's orbit

The out-of-control communications satellite Galaxy 15 is drifting into orbits occupied by other spacecraft.

By Peter B. de SeldingSpace News Staff Writer / May 9, 2010

Intelsat's Galaxy 15 satellite launched in 2005 with an Ariane 5 rocket in Guyana. The communications satellite stopped responding last month, becoming a 'zombie' satellite that now threatens other spacecraft.

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An attempt to shut down the electronics payload of the out-of-control communications satellite Galaxy 15 has failed, leaving the satellite - which ceased responding to ground commands last month - still in its uncontrolled "zombiesat" drift toward orbits occupied by other spacecraft, the satellite's fleet operator Intelsat said Tuesday.

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Galaxy 15 is closing in on the geostationary orbital slot occupied by another C-band satellite, the AMC-11 spacecraft operated by SES World Skies, and with its stuck-on communications payload will be in a position to cause potentially severe interference with the SES satellite during a two-week period starting around May 23, according to Intelsat and SES estimates.

The unsuccessful attempt to shut down the so-called "zombiesat" – a satellite industry term for failed satellites in orbit - occurred on Monday.

IN PICTURES: 'In orbit'

In a Tuesday statement in response to Space News inquiries, Intelsat said it is researching other ways to shut down Galaxy 15 once the satellite has passed through the AMC-11 position and enters — for a limited period of time — a stretch of orbital terrain unoccupied by other C-band spacecraft.

"We do not have an additional specific technical attempt identified at this time," Intelsat said in the statement. "But we will not give up, and expect to have other options to pursue at that time. We are now cooperating with other operators and customers to minimize potential service disruptions caused by interference."

Galaxy 15 stopped responding to ground commands April 5 and since then has drifted out of its 133 degrees west longitude orbital slot on an eastward path along the geostationary arc at around 36,000 kilometers above the equator.

After sending between 150,000 and 200,000 commands to the satellite to coax it back into service, Intelsat was forced to scrap its satellite-recovery efforts and to resort, on Monday, to a limited-duration effort to force the satellite to shut down its transponders. This was to be accomplished by sending a stronger series of signals designed to cause Galaxy 15's power system to malfunction and force a shutdown of the satellite's payload.

That attempt, which Luxembourg-based, Washington-headquartered Intelsat had viewed as its last, best-understood option for Galaxy 15, was unsuccessful. With the satellite now nearing AMC-11, Intelsat is limited in what it can do besides assure itself of the satellite's location. "There is no active testing of the payload," the company said in its Tuesday statement.

Sending radio signals strong enough to force a satellite to shut down could pose dangers to other spacecraft in the target area, which is why Intelsat had only a short window of time to "pulse" Galaxy 15 with signals intended to trigger a failure of its power system. That period lasted about 30 minutes on Monday.